Method and apparatus for joining plastic pipe

ABSTRACT

A simpler method and apparatus for joining plastic pipe ( 2 ) is provided by creating a flange ring ( 4 ) on the end of a plastic pipe ( 2 ), the flange ring ( 4 ) being cut from a short length of a larger dimension plastic pipe selected or machined to fit closely over the outer diameter of the plastic pipe ( 2 ) to provide a flange ( 4 ) which may be bolted or fastened to a similar flange. A similar method may be used to provide a connection by means of a coupling.

This invention relates to improvements in making joints for plasticpipe. In particular, it relates to an improved method for fabricatingand using a means for joining lengths of plastic pipe to form apipeline.

In many aspects of construction and fluid handling, plastic pipe hassubstantially replaced steel and concrete for both above ground andbelow ground installations.

Among the many advantages of plastic pipe is the ease by which it isfabricated (generally by extrusion into lengths of more or less 40feet). Even at such lengths and nominal sizes of substantial diameter,such pipe is relatively light and easy to transport. It is also flexibleand easier to install in difficult locations such as the relining ofunderground conduits.

The easy advantages of manufacture and installation tend to drawattention to the one aspect of plastic pipe which requires more care,attention, and technical know how which is the means by which lengths ofplastic pipe are joined together. Traditionally, this has been done byconventional methods. One method, which is substantially confined tosmall diameter pipe, involves using a socket coupling into which theends of the joining pipes can be fitted and fused or cemented. This isgenerally restricted to small diameter pipe and requires a specialsocket coupling which is specially manufactured to fit over the outerdiameter of the adjoining pipe and therefore requires specialmanufacturing by moulding or machining techniques.

Another conventional method is known as “butt-fusion” which involvesplacing the adjoining ends of two lengths of pipe in close proximity,supporting them in alignment by a machine which includes axially alignedclamps, machining a smooth end on each pipe end by a rotary tool,heating the opposing ends of pipes to the melting temperature of theplastic, and then forcing the two ends of the pipe together in alignmentso that the plastic is welded together by heat and pressure. Thistechnique is difficult in that it requires machines capable of handlingspecific sizes of pipe, and the operation must often be performed on ajob site in cold or inclement weather, and in the awkward location of aconstruction site. Furthermore, it requires a certain amount of skill byconstruction workers who are not necessarily well trained. Thistechnique is more often used for large diameter pipes where thealternative would be to mould or machine special end fittings which areexpensive.

Another method involves the use of “stub-ends”. This is a fitting whichis adapted to be attached to the end of a length of pipe and has a tailpiece corresponding to the size of the pipe and a flange which isadapted to be bolted or otherwise fastened to a matching flange on thenext adjacent pipe. These stub-ends, however, have to be moulded ormachined specifically for the purpose and are therefore costly in termsof manufacturing and inventory.

U.S. Pat. No. 5,462,706 (McMillan et al) discloses forming a flange onan end of a plastic pipe liner wherein a preformed synthetic disc isheat welded to an end of the liner. The liner lines an inner surface ofa steel pipe and is not a free standing pipe. The disc is not whollycylindrical, and does not have a wholly cylindrical outer side. The discis in the form of a stepped ring with a transition from a large diametermain portion to a smaller diameter hub that is fitted over an end ofliner protruding from an end of the steel pipe. After heat welding, thehub and part of the protruding end of the liner are severed to form afinished surface coplanar with the remaining lateral face of the largediameter main portion of the disc.

It is therefore the purpose of this invention to provide a means forjoining lengths of plastic pipe, usually, but not necessarily,polyethylene, which is efficient, inexpensive and efficient whileproviding adequate reliability and safety.

It is the additional purpose of this invention to provide a means forjoining lengths of plastic pipe which does not require specificallymoulded or machined connectors of the type traditionally used.

It is also the purpose of this invention to provide means for joiningplastic pipe which means may be prefabricated in a factory or workshopwhere the working conditions, machinery, technical personnel areavailable to ensure a reliable product, and the ease of connecting pipesat the job site is made quicker and easier.

The invention also provides means to replace traditional manufacturingtechniques to produce common end fittings such as stub-ends, flangeadaptors, reducers, side wall fittings, and other products with aminimal amount of machining and less material.

These objects and other advantages are provided by the present inventionby creating a flange ring on the end of a length of plastic pipe to bejoined, the flange ring being created by cutting a short length of alarger dimension of plastic pipe such that the interior dimension of thering may be chosen or machined to fit snugly over the outer dimension ofthe length of pipe to be joined. Identical lengths of pipe may be joinedby bolts passing through holes in adjacent respective flanges ofadjoining pipe lengths. Similarly, connections may be made by creating acoupling from a length of pipe in which the internal diameter isselected or machined to be the same as the external diameter of thepipes to be joined and adjacent ends of adjacent pipes may be insertedinto the coupling. In most cases the flange or couplings are fused tothe end of a length of pipe by heat.

The present invention may be better understood by reference to thefollowing description of one embodiment thereof with reference to theattached drawings in which:

FIG. 1 is an end elevation view of a pipe connection in accordance withthe present invention;

FIG. 2 is a longitudinal vertical cross-section thereof of theconnection in FIG. 1;

FIG. 3 is a longitudinal cross-section thereof showing the two partswhich form the pipe joint fitting;

FIG. 4 shows the parts in FIG. 3 assembled;

FIG. 5 is an end elevation view of a pipe connection shown inlongitudinal cross-section in FIG. 5A;

FIG. 6 is an end elevation view of a variation of the pipe connectionshown in FIG. 5 with modifications as shown in cross-section in FIG. 6A;

FIG. 7 is a longitudinal cross-section of a full length of pipe havingjoint connectors at each end in accordance with the present invention;

FIG. 8 shows means for assembly of two pieces of a connector fittingsuch as shown in FIG. 3;

FIG. 9 shows the present invention used in an elbow fitting;

FIG. 10 shows a longitudinal section of a connection between pipes ofdifferent size to form a reducer, and FIG. 10A shows a reducerconnection machined for streamline flow;

FIG. 11 illustrates the use of a heating element for fusion assembly ofthe pipe connectors in accordance with the present invention.

FIG. 12 illustrates the use of a heating element to assemble a modifiedversion of the connector made in accordance with the present invention.

In FIGS. 1 and 2 a length of pipe 2 of nominal or conventionaldimensions is shown. This may be a full length of pipe at 40 or 50 feetin length or it may be a short piece 6 inches or 1 foot long of the pipeof the same dimension as used in forming a pipeline. At one end of thepiece of pipe 2 is a flange 4 comprising a surrounding ring and havingbolt holes 6 extending therethrough in a longitudinal direction,parallel to the axis of the pipe.

At this point it should be appreciated that if another piece of pipe ofa similar flange was placed in abutment along the common plane 8 in amirror image orientation, the two sections could be joined together bybolts extending through the bolt holes 6 in a manner similar to theillustration in FIG. 5A referred to later.

FIG. 3 illustrates the assembly of a connector fitting in which thepiece of pipe 2 is connected to the flange ring 4 (as illustrated inFIG. 4) and secured there by fusion which involves the heating of theexternal surface of the pipe 2 and the internal surface of the flange 4to a temperature which allows them to fuse together when the two piecesare joined. Heating can be accomplished in a variety of ways known inthe industry which include electrofusion, radiant heating, socketfusion, and hot air, etc., or the pieces may be joined by extrusionwelding.

Of course, it will be realized that the bolt holes 6 may be bored beforeor after the assembly of the flange, but need to be aligned in adjacentconnectors.

FIG. 5 is an end elevation view of an assembled joint connecting twopieces of pipe together as shown in longitudinal cross-section in FIG.5A. In FIGS. 5 and 5A the two pieces of pipe 2 are joined by bolts 10which pass the bolt holes 6 and compress the flanges together so thatthe ends of the pieces of pipe 2 are separated only by a gasket 12 whichprovides a tight seal. Once again, it should be realized that the piecesillustrated at 2 may be short pieces of pipe capable of being attachedto a conventional length of polyethylene pipe in a factory, or mayrepresent a complete length of such pipe itself, as seen in FIG. 7.

FIGS. 6 and 6A illustrated in elevation and cross section a connectionto those shown in FIGS. 5 and 5A except that for strength and rigiditythe flanges 4 are backed by steel rings 14 respectively on the outboardside of the connecting flanges remote from the adjacent pipe ends. Thismay be used whenever the mechanical strength or the pressure to behandled by pipeline and requires the joint to be more rigid.

Although flange type pipe connectors have been used in the past in bothsteel and plastic, these have previously involved, in the case ofplastic, moulding a single piece of plastic in a shape which providesboth the flange and the tail piece (such as the pipe piece 2) in asingle part which must be designed specifically for the particular sizeand type of pipe to be connected and is therefore time consuming andexpensive to manufacture and keep in stock. Alternatively, suchconnecting pieces are made by forming a large dimension thick wall(heavy gauge) piece of plastic which is later machined to provide a tailpiece corresponding to the pipe to which it is intended to be joined anda larger portion forming the flange. This again is labour intensive andexpensive, and requires a variety of ports to be kept in stock to fitvarious pipe diameters and gauges. These special fittings still need tobe attached to respective ends of a length of standard pipe.

By means of the present invention, this process is made more efficient,cost effective and more easily performed in a workshop environment. Byway of illustration, if the piece in FIG. 3 represents a full length ofplastic pipe at more or less 40 feet in length and has a nominal size of4 inches with an outer diameter (OD of 4.500 inches), the ring 4 may befabricated by cutting a one or two inch length of six inch pipe whichhas an internal diameter (ID) of 4.395 inches, just slightly smallerthan the OD of the 4 inch pipe. This ring can then be machined toapproximately 4.500 inches ID so that it will fit snugly over the end ofthe 4 inch pipe length.

To secure it, the outer end surface of the pipe and the inner surface ofthe ring flange are heated to the melting temperature of polyethylene(or other plastic), and the pieces are fitted together to form theassembled flange end show in FIG. 4 (with or without the bolt holes).

Similarly, a length of pipe with an OD of 16 inches can be fitted with aflange ring cut from a piece of 20 inch stock with an ID of 15.289inches prior to machining.

It will be realized that in a factory that manufactures lengths of pipeof various diameters and wall thickness, or in a supply warehouse thatstocks a wide variety of plastic pipe, such compatible pieces will berelatively easy to acquire.

Furthermore, providing lengths of pipe with the appropriate connectingflanges can easily be accomplished in an indoor machine shop in whichthe right atmosphere, tools, and personnel are available, and the flangerings can be easily machined and assembled.

FIG. 7 illustrates a length of standard pipe fitted with the flangesdescribed above which may be provided for a specific job or manufacturedto be available in stock as needed.

No illustration of the method or machinery for machining the flange ring4 is provided since these techniques are well known in the industry.

FIG. 8, however, illustrates the method by which a snug fitting pipepiece 20 may be mechanically forced into the ID of a flange ring 40under hydraulic pressure, if necessary, as it may well be in the case ofvary large diameter pipe with a large wall thickness.

FIG. 9 illustrates how elbows and other fittings may be fabricated usingthe same technique.

FIG. 10 illustrates how a reducer may be formed which would serve toconnect a length of 6 inch pipe to a length of 4 inch pipe using thesame technique. FIG. 10A illustrates the reducer connection aftermachining to make the transition between the large diameter and smalldiameter, less abrupt and more streamlined.

It has been previously mentioned that conventional techniques for fusionof plastic pipes involve the use of machines to hold the adjacent endsin position and in alignment while a disk shaped heating element is usedto heat the respective ends of the pipes to a melting temperature beforethey are fused together.

FIG. 11 illustrates the use of a heating element to assemble a connectorfitting. A length of pipe 2 is held by a clamp 25 adjacent to a heatingelement 30, which is usually made of aluminium for its thermalconductivity properties. The heating element 30 has a raised ring 32 onone side which is sized to fit over and melt the outer surface of theend of the pipe 2. On the other side of the heating element 30 is araised disk 34 which is sized to fit into and heat the inner surface ofthe flange ring 4 which is in turn held by another clamp 27. Althoughnot illustrated, the clamps 25 and 27 are mechanically or hydraulicallycontrolled so that they can move the pipe and the flange ringrespectively into contact with the heating element and then subsequentlymoved apart from the heating element while the heating element iswithdrawn and then the clamps are used to force the pipe and flangetogether into the assembled position illustrated in FIGS. 3 and 4.

FIG. 12 illustrates a modified version of the assembly in FIG. 11 inwhich the length of pipe 2 is heated and fitted to a ring 44 of greaterlongitudinal dimension than the ring 4. As illustrated in FIG. 12A, pipe2 is fused to the ring by insertion into half of the length of the ringleaving the other half available to receive the opposite end of the nextadjacent pipe thereby forming a coupling where no bolts are required.

As previously mentioned, this may be done in an assembly line manner ina manufacturing or workshop facility.

It should also be realized that where the manufacture and use of plasticpipe in large volumes justifies the investment, it may be possible todesign a series of standard sizes in which the OD of each nominal pipesize is substantially equal to the ID of the next largest nominal sizeso that the ring flanges 4 can be easily manufactured by slicing a pieceof the appropriate pipe without the need for sizing or machining.

Furthermore, the reducer fitting as illustrated in FIGS. 10 and 10A maybe fabricated simply by heating the ends of two compatible sizes of pipebefore joining them in the illustrated manner.

It will, of course, be realized that numerous modifications andvariations may be applied to the illustrated embodiments withoutdeparting from the inventive concept herein.

1. A method of joining lengths of plastic pipe comprising: selecting apiece of pipe having an internal diameter equal to or slightly less thanthe outer diameter of the pipe to be joined; cutting short lengths ofsaid piece of pipe to form rings; machining the internal diameter ofsaid rings, if necessary, to enable said ring to fit snugly over theouter diameter of said lengths of pipe; heating the external surface ofan end of each of said lengths of pipe and the internal surface of saidrings to a melting temperature; fitting one of said rings over the endof each of said lengths of pipe to form a flange; and joining saidlengths of pipe together by fastening adjacent flanges of adjacent pairsof said lengths of pipe together.
 2. A method as claimed in claim 1including the steps of providing holes in said flanges parallel to thelongitudinal length of the pipe and passing bolts through matching holesin adjacent lengths of pipe to fasten said flanges together.
 3. Methodof forming a length of plastic pipe adapted to be joined to a furtherlength of plastic pipe, comprising: providing a first length of plasticpipe having an outside diameter; selecting a second length of plasticpipe having an inner surface with an inside diameter equal to orslightly less than said inner surface to fit snuggly over said outsidediameter; cutting a short length of said second length of pipe to form aring, applying said ring as a flange on said outside diameter; andfastening said flange to said first length of pipe; and includingproviding said flange with a series of bolt holes extending in adirection parallel to the longitudinal axis of said first length ofpipe.